This invention relates to containers, tanks or ships, for the storage or transportation of cryogenic liquids such as liquid natural gas (LNG), and is particularly concerned with containers, tanks or ships of the above type containing non-metallic, e.g. plastic, foam insulation and one or more liners, and preferably a low temperature resisting, i.e. low thermal expansion, liner such as nickel steel, and a support system for the liner or membrane, in conjunction with the foam insulation layers.
A container or tanker for the storage and/or transportation of a cryogenic liquid must be designed to withstand extremely cold temperatures. Generally vessels of this type are composed of an outer wall of a rigid structure, a heat insulating layer provided at the inside surface of such wall and an inner membrane on the inside surface of such heat insulating layer. Often several heat insulating layers of non-metallic, e.g., plastic, foam insulation, are employed and one or more membranes, an inner liner or membrane such as a nickel steel liner in contact with the cryogenic liquid and one or more additional secondary liners positioned between foam insulation layers. The primary liners, generally made of a thin low temperature resistant (low thermal expansion) material such as nickel steel, is maintained in close contact with the surface of the adjacent heat insulating layer and transmits the internal pressure applied by the low temperature liquefied gases through the heat insulating layers to the outer container or the hull of a tanker.
Of particular importance, the container or its insulation system must be capable of withstanding the thermal strains induced by the cold liquid and the transients during the cooling and warming cycles caused by the loading and unloading of the liquid, and the mechanically induced strains from the ship hull or container displacement during operation. The magnitude of such thermal strains induced when cooling most materials, in a restrained condition, to cryogenic temperatures is sufficient to cause yielding of the material, particularly the thin metal membranes employed as liners. This yielding will result in fracture and failure of such materials on subsequent warming and cooling cycles resulting in a failure of the system. Many designs and materials have been proposed to solve this problem. However, generally the solution to this problem has resulted in relatively complex membrane support systems which are often difficult to fabricate and are expensive.
Illustrative of the prior art in this respect are the following patents. U.S. Pat. No. 3,724,703 discloses a low temperature liquefied gas storage tank and tanker comprising a heat insulating layer of polyurethane foam, a thin liner, e.g. of nickel steel, and a vacuum pump to detect leaks. U.S. Pat. No. 3,489,311 discloses a multilayer foam insulation system, employing grooves or precut channels in the insulation and a vacuum pump as part of a leak detection system U.S. Pat. No. 3,341,049 discloses a multilayer insulation system including honeycomb panels, and employing an expansion joint to connect the honeycomb panels and form a seal at the primary linear. U.S. Pat. Nos. 3,931,424; 3,882,591; 3,319,431; 3,692,205; 3,694,986; and 3,341,051 are further illustrative of the prior art with respect to support systems for the foam insulation and the linear or membrane in cryogenic tanks.